[bugpoint] Update runPasses to take ArrayRef instead of a pointer (NFC)

This makes it slightly easier to pass extra arguments to runPasses
and simplifies the code slightly.

Reviewers: efriedma, bogner, dblaikie, diegotf, hiraditya

Reviewed By: dblaikie, hiraditya

Differential Revision: https://reviews.llvm.org/D68228

llvm-svn: 373265